For those that can't wait until Killzone 2 launches on February 27th, the single-player demo became available for all of those who have pre-ordered Killzone 2 from GameStop.
Those that pre-ordered in-store should be able to use the voucher card, while those that pre-ordered through GameStop.com should receive your redeemable code later today (we actually got ours last week).
They've also teased Killzone 2 fans over on the PlaystationBlog with an official Killzone 2 Helghast Rifle Replica... They haven't released the details of how to get our hands on one, but as soon as they do we'll let you know!
UPDATE! For those that aren't able to find the demo in the Playstation store, it's because you have to pre-order the game from GameStop and have a promotion code from them.
Here's the instructions (assuming you have a code):
1. Open an account on the PlayStation Network (or use an existing account).
2. From the PlayStation Network icon on the Xross Media Bar, select 'Account Management'.
3. Select 'Redeem Code'.
4. Enter Promotion Code. Please note that the Promotion Code is case sensitive and must be entered exactly as displayed.
5. Once the Promotion Code has been entered correctly, click 'Continue'. Once you accept the terms you will be taken to the download screen.